Threaded tubular joint proof to external pressure

ABSTRACT

A threaded pipe connector which may find application in the petroleum and gas industry, and pipe connections formed with the connector. The connector includes a male element disposed at the end of a first pipe and a female element disposed at the end of a second pipe. The male element is provided with an external tapered male threading and the female element is provided with an internal tapered female threading corresponding to the male threading. A central seal, formed by a male bearing surface and a female bearing surface and bearing against each other and disposed in a central zone of the male and female threading respectively where the threadings have been interrupted, seals the connector when the connector is assembled. The connector and the connected pipes formed from this connector provide a tight seal under high external pressures.

FIELD OF THE INVENTION

The present invention relates to a threaded connector for pipes, moreparticularly for steel pipes which is intended for the petroleum and gasindustry and for connecting pipes produced from this connector, ofparticular importance because of its tight seal against high externalpressures.

The present invention relates to a threaded connector for pipes, moreparticularly for steel pipes which is intended for the petroleum and gasindustry and for connecting pipes produced from this connector, ofparticular importance because of its tight seal against high externalpressures.

DESCRIPTION OF THE RELATED ART

Pipe connectors used in the petroleum and gas industry are known inwhich the junction is constituted by an externally threaded male elementwhich screws into an internally threaded female element, the two maleand female threads mating with each other. Such connectors are used toproduce extraction pipe strings or casing pipe strings for petroleum andgas wells.

Pipe connectors used in the petroleum and gas industry are known inwhich the junction is constituted by an externally threaded male elementwhich screws into an internally threaded female element, the two maleand female threads mating with each other. Such connectors are used toproduce extraction pipe strings or casing pipe strings for petroleum andgas wells.

Depending on the severity of the conditions of the petroleum and gasexploitation wells, the basic structure of the connectors describedabove is completed in known manner by providing them with a variety oftypes of sealing means such as rings of synthetic material or metallicsurfaces which bear on each other.

An example which can be cited is described in European patent EP 0 488912 which describes a tapered threaded connector provided with a maletapered surface in the zone located after the male thread close to thefree end of the male element, and in the corresponding zone of thefemale element with a corresponding female tapered surface, this pair ofmale and female surfaces bearing on each other when the connector is inthe made up position forming an internal sealing surface against fluidcirculating inside the pipes. The connector described in EP 488 912 isalso provided with an abutment which enables the two male and femalethreaded elements to be precisely positioned with respect to each otherwhen making up.

For certain applications, the connectors must resist and remain sealedboth to the internal fluid pressure circulating in the pipe and to theexternal pressure existing outside the pipe. Such a seal is critical forthe reliability of the connector when the external pressure is high (forexample over 600 bars), whether the fluid concerned is a liquid or a gasor a mixture of the two. In this case, beyond a given pressure theinternal sealing surface such as that described in EP 488 912 cannotresist fluid penetration which advances from the exterior to theinterior along the thread and can then deform or even break the male lipon which said internal sealing surface is located, and it thusinfiltrates into the interior of the pipe.

To overcome this problem, it has been proposed to provide the type ofconnector described in EP 0 488 912 with a sealing surface located closeto the free end of the female element.

French patent FR 77 12851 thus describes a connector provided with aninternal sealing surface close to the free end of the male element andwith an external sealing surface close to the free end of the femaleelement. It should be tight to internal and to external pressure.However, according to FR 77 12851, each of those two sealing surfaces isassociated with an abutment, which renders the function and manufactureof the connector much more difficult. Abnormal deformations can occurwhen dimensional tolerances are not entirely adhered to or when themakeup torque is too high, which deformations can fundamentally modifythe function of the two sealing surfaces and cause them to losetightness as regards the fluid inside the pipe and the fluid outside thepipe.

Producing such a connector is expensive, firstly because of themachining tolerances required for it to function properly and secondlybecause of the quantity of material necessary to produce both aninternal sealing surface and an external sealing surface, requiring theuse of thicker pipes.

The prior art also discloses connectors in which the male and femaleelements comprise a tapered or straight threading constituted by tworadially and axially offset independent threaded zones (such threadedzones can also be termed steps) which are provided with sealingsurfaces.

Such is the case in EP 0 767 335 which describes a connector whichcomprises a tapered threading with two independent radially and axiallyoffset threaded zones, with an internal sealing surface close to thefree end of the male element and an external sealing surface close tothe free end of the female element. However, because of the situation ofthe external sealing surface close to the free end of the femaleelement, this sealing surface cannot resist very high pressures as thereis not sufficient material at the end of the pipe to keep said surfacerigid.

Further, EP 0 149 612 describes a connector which comprises a threadingwith two radially and axially offset independent threaded zones withdifferent tapers between which a sealing surface is provided constitutedby male and female surfaces in bearing contact during makeup, thatconnector also comprising an internal sealing surface close to the freeend of the male element and an oblique abutment at the free end of themale element.

Because of the structure of the two radially and axially offsetindependent threaded zones, the connector of EP 0 149 612 requiresrelatively thick pipe walls and because of the corresponding cost andbulk, it is difficult to envisage it being produced in the form of acoupling.

BRIEF SUMMARY OF THE INVENTION

The present invention seeks to provide a threaded pipe connector which,while being tight to external pressure, does not have the disadvantagesof the above connectors.

The present invention seeks to provide a threaded pipe connector which,while being tight to external pressure, does not have the disadvantagesof the above connectors.

Thus a connector is sought which is tight at high external pressureswhile remaining tight to internal pressure and which is simple, robustand economical both as regards the quantity of material and thethickness of the pipes which are required, and as regards machining.

The term “robust” means a connector which can resist high pressures, forexample of the order of 600 bars to 1500 bars, and which is easy toassemble on-site.

The production of a threaded pipe connector has also been sought, whichconnector differs as little as possible from connectors which alreadyexist, where the threading is constituted by a single threaded zone incontrast to threaded connectors wherein the threading comprises twoindependent axially and radially offset threaded zones, and which can beproduced from such connectors with a single threaded zone withoutmodifying the structure of the assembly.

A connector which has a single sealing means which can be used bothagainst internal pressure and against external pressure has also beensought.

The connector of the invention is intended for the production ofpipelines or strings.

Its field of application is not limited to the petroleum and gasindustry but extends to any application where the.same types of problemsoccur or can occur.

A non limiting example is geothermal liquid or vapour water extraction.

The connectors are produced from any metallic materials, for examplesteel or ferrous or non ferrous alloys in particular with the desiredmechanical characteristics and with the corrosion strength required forthe envisaged application.

The threaded pipe connector of the invention is of the type comprising amale element disposed at the end of a first pipe and a female elementdisposed at the end of a second pipe.

The male element comprises an external male threading constituted by asingle male threaded zone and the female element comprises a femalethreading constituted by a single female threaded zone, the malethreaded zone corresponding to the female threaded zone such that theycan be made up one into the other.

The male and female threading are tapered and a stop means can stopmakeup of the connector at a set position.

A sealing means is interposed between the male and female element, whichmeans is constituted by a male bearing surface on the male element and afemale bearing surface on the female element, these two bearing surfacesbeing capable of coming into bearing contact with each other when theconnector is made up and being respectively disposed in a globallycentral zone of the male threaded zone for the male bearing surface anda globally central zone of the female threaded zone for the femalebearing surface in which the respective male and female threadings areinterrupted.

The term “globally central zones” of the male threaded zone and of thefemale threaded zone in which the male and female threadings areinterrupted means a zone which is substantially at the mid point alongthe axis of the connector of the male and female threaded zone or in aportion which extends to either side of the mid point along the axis ofthe connector of the male and female threaded zone by a length of atmost ¼ of the length along the connector axis of the threaded zone.

Advantageously, the male threaded zone and the female threaded zone willbe considered to encompass both perfect threads and imperfect orvanishing or incomplete end threads.

In the following text, this sealing means will simply be termed the“central sealing means”, it being understood that this term must not beinterpreted restrictively having regard to the information provided.

The stop means which can stop makeup of the male element in the femaleelement in a set position can be constituted either by means linkeddirectly to the threadings or by means which are independent of thethreadings.

Since the threadings are tapered, they naturally have an interferencefit, and the stop means directly linked to the threadings can beconstituted, as is already known, by makeup to a pre-set torque or bytwo marks, one located on the male element and one on the femaleelement, which coincide at the end of makeup.

Regarding means which are independent of the threadings, the stop meanscan be an abutment which, in the desired position, opposes continuedrelative makeup of the male element into the female element.

Depending on the envisaged service conditions for the connector of theinvention, the connector may comprise only one single sealing means asdescribed above, the central sealing means, or in addition to thiscentral sealing means it may also comprise a second sealing means.

This second sealing means is advantageously a means which is known perse such as a metal-metal bearing contact ensured by two bearing surfacesrespectively disposed one close to the free end of the male element andthe other on the corresponding portion of the female element.

The bearing surfaces of the central sealing means can be of any type orform provided that they can come into bearing contact with each otherduring makeup of the connector.

As an example two cylindrical surfaces can be used, the male bearingsurface being of a slightly higher diameter than the diameter of thefemale bearing surface to ensure an interference fit of the two surfaceswhen made-up, creating the seal.

It is also possible to use at least one cylindrical surface, the othersurface being toric, for example, or of any nature which can bring aboutan interference contact with the former.

The male bearing surface and the female bearing surface do notnecessarily have the same type of geometry.

Advantageously, at least one of the bearing surfaces of the centralsealing means, the male surface or the female surface, is constituted bya tapered surface the taper of which is in the same direction as thethreading taper but wherein advantageously the angle with respect to thecommon axis of the male element and the female element is higher thanthe angle of the thread taper with respect to this axis.

By way of non limiting example, the contact distance between the maleand female bearing surfaces of the central sealing means can be in therange 1 to 10 mm.

The threadings of the male and female elements can be of any type, suchas for example triangular or trapezoidal API (American PetroleumInstitute) threadings, the latter ones being termed “buttress” by theAPI, world known designation and the use of which is common to the manof art to design said type of threadings.

In the case of a buttress threading, they may have negative load flanks,in particular when associated with an abutment, to enable the threadingsto engage together better.

The present invention also relates to a threaded connection for twopipes using the connector of the invention, the structure of which hasbeen described above.

A number of variations are possible.

In a first variation, the connection is integral, each pipe to beconnected carrying alternately at each of its ends a male element and afemale element of the connector of the invention, as described above.

Thus the integral connection of two pipes is carried out by screwing themale element at the end of a first pipe into the female element at theend of a second pipe.

Depending on the configuration and thickness of the pipes, it may beadvantageous to form the female element on the end of a pipe where theexternal diameter has previously been expanded, the male element beingproduced on a pipe the end of which can if necessary have beenthickened, for example by hot forming.

In a second variation, the connection for two pipes is of the coupledtype, i.e., produced using a coupling joining the two pipes, and employstwo connectors of the invention, the structure of which has beendescribed above.

In this case, a male element as described above is formed at each pipeend and a female element as described above is formed at each end of acoupling, the two male elements at the two ends of two pipes to beconnected being screwed into the two female elements of the coupling.

In this case, the free ends of the two pipes to be connected can, in afirst embodiment, come into a bearing relationship with each otherinside the coupling at the end of makeup, thus constituting an abutmentwhich can stop makeup at the set position.

In a second embodiment of the coupled connection, the free end of eachpipe comes into a bearing relationship with a stop-lug provided in thecentral portion of the coupling.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures and examples describe non limiting examples ofthe connectors and connections of the invention.

The accompanying figures and examples describe non limiting examples ofthe connectors and connections of the invention.

FIG. 1 shows a partial axial cross-section of the male and femaleelement of a threaded connector of the invention in a non-connectedposition.

FIG. 2 shows the connector of the invention of FIG. 1 in the connectedposition.

FIG. 3 shows a partial axial cross-section of the connector of theinvention in the connected position, this connector being a variation ofthe connector of FIG. 2.

FIG. 4 shows a partial axial cross-section of the connector of theinvention in the connected position, this connector being a furthervariation of the connector of FIG. 2.

FIG. 5 is an enlarged representation of portion I of FIG. 2 showing afirst embodiment of the central sealing means of the connector of theinvention.

FIG. 6 is a variation of FIG. 5 and shows a further embodiment of thecentral sealing means of the connector of the invention.

FIG. 7 is a further variation of FIG. 5 and shows a further embodimentof the central sealing means of the connector of the invention.

FIG. 8 shows an axial cross section in the connected position of athreaded and coupled connection of the invention using two threadedconnectors of the invention, the coupling comprising a central stop-lug.

FIG. 9 shows an axial cross section in the connected position of afurther threaded and coupled connection of the invention, which uses twothreaded connectors of the invention, the coupling not having a centralstop-lug.

FIG. 10 shows an axial cross section in the connected position of astill further threaded and coupled connection of the invention whichuses two threaded connectors of the invention, the coupling not having acentral stop-lug.

FIG. 11 shows a partial axial cross-section of the male element on oneend of a pipe that has been thickened, and the female element at one endof a pipe that has been expanded, of a threaded connector in anon-connected position.

FIG. 12 shows the connector of FIG. 11 in the connected position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to represent the invention better, the accompanying Figures aredeliberately diagrammatic; the dimensions, angles and the ratios of thedimensions are not necessarily respected, some of the dimensions beingconsiderably exaggerated.

FIG. 11 shows a partial axial cross-section of the male element 1 on oneend of a pipe that has been thickened, and the female element at one endof a pipe that has been expanded, of a threaded connector in anon-connected position.

FIG. 12 shows the connector of FIG. 11 in the connected position.

In order to represent the invention better, the accompanying Figures aredeliberately diagrammatic; the dimensions, angles and the ratios of thedimensions are not necessarily respected, some of the dimensions beingconsiderably exaggerated.

FIGS. 1 and 2 show a partial axial cross section through a plane passingthrough their common axis X1—X1 of a male element 1 and a female element2 respectively disposed at the end of a first steel pipe 3 and a secondsteel pipe 4 of a threaded connector 5 of the invention.

These male and female elements 1, 2 are shown connected in FIG. 2,connector 5 being in its made up position. FIG. 1 shows them beforemakeup.

To better illustrate the connector before connection, female element 2is shown radially offset from its axis X1—X1 in FIG. 1.

The external diameter of end 6 of pipe 4 on which female element 2 isformed is greater than the diameter of the continuing portion 4 of thepipe, this diameter at 6 having been produced by expanding the pipe end.

Male element 1 comprises an external male threading 7 constituted by amale threaded zone Fm. Threading 7 is tapered and is diagrammaticallyrepresented, as is the custom, by the two tangential generatrices of thethreadings respective to the thread crests and roots.

This threading 7 is produced on a single taper and the thread has aknown geometry and is of a type which is suitable for the desiredapplication for the connector and its service conditions.

In contrast to threaded connectors where the threading comprises, oneach male and female element, two radially and axially offsetindependent threaded zones (or two threaded steps), such as in theconnector described in EP 0 767 335, the connector of the presentinvention is defined as a connector with a threading constituted by asingle threaded zone.

Thus male threaded zone Fm is considered to be a single male threadedzone the length Lm of which covers the axial length of the threadingfrom one end to the other, this length including the imperfect orvanishing or incomplete threads at the ends.

Female element 2 has an internal tapered female threading 8 whichcorresponds to male threading 7 and is constituted by a single femalethreaded zone Ff, shown in analogous fashion to threading 7.

It comprises a single threaded zone the length Ff of which covers theaxial length of the threading from one end to the other, this lengthincluding the imperfect or vanishing or incomplete threads at the ends.

A central sealing means 9 is interposed between male element 1 andfemale element 2 at threadings 7, 8.

This means 9 is constituted by a male bearing surface 10 and a femalebearing surface 11 respectively disposed in a globally central zone ofthe male threaded zone Fm and the female threaded zone Ff where therespective male and female threadings have been interrupted, these twobearing surfaces 10 and 11 being capable of coming into mutual bearingcontact in the connected position of the connector as shown at 9 in FIG.2.

Thus the metal-metal contact pressure between surfaces 10 and 11 createsa seal in the form of a continuous annular surface which resists anypenetration of fluid from the exterior of pipes 3, 4 to the interior orvice versa.

The term “globally central zone of the male threaded zone Fm and femalethreaded zone Ff” means a zone situated mid-way along lengths Lm and Lfor a zone which extends either side of the mid point of lengths Lm andLf by an amount equal to a ¼ of the threaded lengths Lm, Lf, thisposition being selected as a function of the external pressures of thefluids which are to be resisted and of the pipe thickness.

In order for surfaces 10 and 11 to coincide perfectly at the end ofmakeup, the connector of the invention comprises a stop means which canstop makeup at a set relative axial position of male element 1 withrespect to female element 2. In the case of FIGS. 1 and 2, this stopmeans is constituted in a known manner by two marks 12, 13 shown as athick line on male element 12 and on female element 13. Makeup ofelements 1, 2 can be stopped when these marks 12, 13 coincide, as shownin FIG. 2.

These marks 12, 13 are positioned such that a certain interference fitis developed between male threading 7 and female threading 8 as a resultof the tapered form of the threads which enables a thread interferencefit to be produced between male threading 7 and female threading 8.

The term “interference fit” means the positive difference existingbefore makeup at the level of zones Lm and Lf between the radius withrespect to the axis of the connector at a point on the male threadedzone 7 and that of the corresponding point on the female threaded zoneafter makeup.

Advantageously, the interference fit measured with respect to theconnector axis between bearing surfaces 10, 11 is arranged to be atleast equal to and preferably greater than the interference existingbetween threads 7, 8, thus reducing the makeup track for the bearingsurfaces up to the connected position.

Either side of central sealing means 9, the threadings, both of the malethreaded zone Fm and of the female threaded zone Ff, have beeninterrupted such that the connector can be made up and broken outwithout difficulty as will, for example, be seen in FIGS. 5, 6 and 7.

The seal obtained with the central sealing means 9 described above isparticularly effective against high external pressures because the maleand female bearing surfaces 10, 11 in the globally central position aresupported by a sufficiently high thickness of metal with respect to thepipe thickness both in male element 1 and in female element 2.

Advantageously, at least for certain conditions of service, care istaken such that on male element 1, the thickness of the material at thelevel of the male bearing surface is at least 50% of the thickness ofpipe 3.

Such conditions are impossible to satisfy when the sealing surface ofthe connector is located beyond the threading at the end of the maleelement as is the case, for example, in EP 0 488 912.

Increasing the thickness at the level of this bearing for the maleelement causes a problem since the connector would have to have too lowa taper which would cause difficulties as regards engaging the maleelement in the female element and would necessitate a diameter andlength which would be too high and thus too expensive for the femaleelement.

The connector of the invention can be produced from a conventionaltapered threading with a single threaded zone.

Thus much thinner pipes are needed than prior art connectors where thethreading comprises two independent axially and radially offsetthreadings or steps. The connectors of the invention are thus much morecompact, cheaper as regards materials and simpler to machine.

Further, because of the globally central position of the central sealingmeans 9, the male threaded zone can extend to the end 14 of the maleelement with perfect threads, from which point the efficiency of thefemale element 2 is calculated.

Thus the bulk of the connector can be reduced as regards the femaleelement, i.e., the external diameter of this female element 2 can bereduced with respect to a conventional connector provided with sealingsurfaces at the end of the male element.

Similarly, female threading 8 can be prolonged towards the free end ofthe female element until the appropriate external diameter of pipe 3 isattained. Thus the connector efficiency is 100% of pipe 3. This is notpossible with a connector provided with bearing surfaces at the free endof the female element.

FIG. 11 shows a partial axial cross-section of the male element 1 on oneend of a pipe that has been thickened, and the female element 2 at oneend of a pipe that has been expanded, of a threaded connector in anon-connected position. FIG. 12 shows the connector of FIG. 11 in theconnected position.

FIG. 3 shows a variation of the connector of FIGS. 1 and 2.

This connector 15 is shown in the connected position as a partial axialcross section; only the portion above axis X2—X2 is shown.

As with connector 5 in FIGS. 1 and 2, it comprises a male element 16 anda female element 17 which are each provided with a respective male 18and female 19 single tapered threaded zone.

A central sealing means 20 is disposed in the globally central zone ofmale 18 and female 19 threadings, here substantially at the mid point oflength L′f in female threaded zone 19.

The stop means enabling makeup of male element 16 into female element 17to be stopped into a set position is constituted here by an abutment 21formed by an internal shoulder 22 on the female element, the shoulderbeing transverse to axis X2—X2 on which end 23 of male element 16 bears,which end has been provided with the desired shape so that it bears onshoulder 22.

Thus makeup when connecting connector 15 is stopped by abutment 21 whenthe desired makeup torque is reached.

Clearly, matters are arranged so that both the threadings 18, 19 and thecentral sealing means 20 provide an interference fit as a result ofexisting interferences.

If needed, in this case it wilt be possible to use “buttress” type (astermed by the American Petroleum Institute) male and female threadings18, 19 with negative flanks in order to provide better engagement of themale threading 18 in the female threading 19 and thus to place inbearing contact the flanks of the threadings which are on the sideopposite the abutment 21.

FIG. 4 shows an axial partial cross section above axis X3—X3 of afurther variation of the connector of FIGS. 1 and 2.

In its connected position, this connector 24 has a male element 25 and afemale element 26 each provided with a respective male 27 and female 28single tapered threaded zone.

A central sealing means 29 is located substantially mid-way along thelength L″f of the female threaded zone 28. Like the means of FIG. 1,this means is constituted by a male sealing surface and a female sealingsurface bearing one against the other in the connected position.

Here, the stop means enabling makeup of the male element 25 into femaleelement 26 to be stopped in a set position is constituted, in a mannersimilar to the example of FIG. 3, by an abutment 30, the tapered convexshoulder 31 of the female element acting as a bearing surface for thecorresponding concave tapered end 32 of male element 25.

In this case abutment 30 has a re-entrant taper, such an abutment beingknown as such, while in the case of FIG. 3, abutment 21 is perpendicularto axis X2—X2.

Further, connector 24 comprises a second sealing means 33 locatedbetween internal end 34 of male 27 and female 28 ends and the abutment30, which means is constituted by a male convex tapered surface 35 whichin the connected position comes into close bearing contact with acorresponding female concave tapered surface 36.

While the central sealing means 29 can act to ensure a seal againstfluid inside the pipe and against fluid outside the pipe, in someparticularly severe cases it may be important to reserve the centralsealing means 29 as a seal against external fluid and as is the case ofFIG. 4, to provide a second sealing means 33, in this case in the formof sealing surfaces but this is not limiting, which ensures a tight sealagainst internal fluid.

In a variation, this sealing means can be constituted by a sealing ring,for example, a sealing device which is known in itself.

When the connector has a second sealing means such as 33, it is possibleto offset the central sealing means 29 towards the end of the femaleelement.

Advantageously, said central sealing means is kept within the limits ofsegment AB of the female threading with length L″f, A representing themid point of L″f and B being the point located at the mid point of thehalf of L″f on the free end side of female element 26.

When the connector comprises only the central sealing means, for exampleas shown in FIG. 3, if this means is to act both to provide a sealagainst external and internal material, then advantageously the centralsealing means 20 is offset from the central position at the mid length Cof the female threading with length L′f by locating it within segment CDrepresenting ¼ of the length of L′f, the offset this time being towardsthe free end of the male element 16.

In all cases, at the level of the central sealing means (20, 29) in thesectional plane passing through this central sealing means andperpendicular to the axis the trace of which is P1—P1 (FIG. 3) or P2—P2(FIG. 4), it is ensured that a sufficient quantity of material isprovided on the male (h1m, h2m) and female (h1f, h2f) element side tosupport the sealing surfaces.

By way of non limiting example, h1m, h2m and h1f and h2f, whileremaining close to 50% of the thickness of pipe 3, 4, can vary by anamount of the order of 30% to 80% of said thickness.

The values for h1m and h2m may be even slightly higher than 80% of thethickness of the body of the pipe if the diameter of the internalperipheral surface of the male component has been made smaller than thediameter of the body of the pipe, for example by making conical thewalls at the male end.

The next FIGS. 5, 6 and 7 show enlarged versions of zone I of FIG. 2 inseveral variations.

FIG. 5 shows male tapered threading 7 and female tapered threading 8connected and represented by their respective teeth.

By way of non limiting example, the threading is a trapezoidal APIthreading of the “Buttress” type which is known in itself with male 34and female 35 load flanks bearing one on the other, and male 36 andfemale 37 stabbing flanks.

Crests 38 of the teeth of female threading 8 are in an interference fitagainst roots 39 of male threading teeth 7 by interference of thethreads together and correspondingly for the crests of the malethreading which bear against the roots of the female threading.

Clearly, different relationships between the female threading and themale threading can be envisaged but these always produce an interferencefit when made up.

As an example crests 38 of the teeth of female threading 8 can be in aninterference fit against roots 39 of male threading teeth 7 byinterference of the threadings together while the crests of the malethreading do not bear against the roots of the female threading.

G1 and G2 represent the generatrices of cones which define the maximumspatial requirement of male 7 and female 8 threadings. The slope of thegeneratrices has been deliberately exaggerated to facilitatecomprehension.

Both the male 7 and female 8 threading have been interrupted over a setlength to make room for central sealing means 9. This length can vary byan amount of the order of 3 to 5 pitches of the threading.

Male 10 and female 11 bearing surfaces which form the sealing means 9are parallel truncated conical surfaces with generatrix G3 the slope ofwhich is advantageously higher than the slope of the threadings.

The difference a between the slope of generatrices G1, G2 and the slopeof the generatrix of the bearing surfaces G3 is preferably limited to20°.

When the connector is made up, surfaces 10, 11 bear against each otherwith a contact pressure which ensures a seal.

This contact pressure is all the higher as the value of the interferenceat surfaces 10, 11 is higher, this interference causing elasticdeformation which is the source of said pressure.

FIG. 5 deliberately shows surfaces 10, 11 by their geometry beforemakeup so as to represent the real interference between these twosurfaces, namely d1 which is measured perpendicular to connector axisX1—X1. The higher the value of the interference, the higher the contactpressures of the surfaces.

When the surfaces are in contact with a contact pressure against eachother, in the made up state, the contact line is along generatrix G3.

Bearing surfaces 10, 11 are surrounded by clearances 40, 41 which arerequired upstream and downstream to allow the male element to engage inthe female element and makeup without any problems and also to allow themachining tools to disengage.

FIGS. 6 and 7 represent variations of the central sealing means 42, 43.

In FIG. 6, male bearing surface 44 is constituted by a truncated surfacethe generatrix G4 of which is parallel to generatrices G1 and G2 ofthreads 7, 8. The female bearing surface 45 is constituted by a toricsurface.

In FIG. 7, the male bearing surface 46 is toric and the female bearingsurface is truncated with a generatrix G5 which is parallel togeneratrices G1 and G2.

The interferences of the bearing surfaces are shown in FIGS. 6 and 7 atthe point where they are a maximum, namely d2, d3, respectively.

The bearing surfaces shown in FIGS. 6 and 7 have the advantage of beingsurfaces with a makeup track which is shorter than surfaces 10 and 11 inFIG. 5. However, the distribution of the contact pressures whichsurfaces 44/45 or 46/47 develop is different from that for surfaces 10,11.

The surfaces of the male and female bearing covered by the invention canbe of any form provided that they can bear one against the other in theconnected position of the connector.

Advantageously, the maximum bulk of these bearing surfaces is defined bythe space existing between generatrices G1 and G2 which define thelimits of the space requirements of the threading.

In practice, in order to reinforce the effect of the central sealingmeans 9, 42, 43, and/or the mutual bearing of the surfaces 10-11, 44-45,46-47 respectively and also when the connector comprises a secondsealing means such as 33, if needed for possibly reinforcing theefficiency of this second sealing means, one can be led to reduce oreven cancel the radial interference between the thread crests and threadroots of one of the portions of the threadings located on one side ofthe central sealing means.

For that purpose on one of the 2 elements, i.e. on the male element oron the female element of the connector, one can set off, by a distancemeasured with respect to the axis of the connector in the range of 0,005mm to 0,10 mm, the position of the generatrices G1 and G2 by dealingseparately with the portion of the generatrix G1 if one works on themale threading or of G2 if one works on the female threading, saidportion being shown in figures such as 5, 6, 7 on the left side of thecentral sealing means, and with the portion of generatrix G1 or G2 whichis shown in figures such as 5, 6, 7 on the right side of the centralsealing means.

In such a way both portions of generatrix G1 or G2, that is to say theportion which is situated on the left side of the central sealing meansand the portion which is situated on the right side, remain parallelwhile being slightly radially offset by the quantity indicated withrespect to the axis of the connector.

The global functioning of the connector which has just been describedimmediately above and which remains fundamentally based on a singlefemale threaded zone and on a single male threaded zone such as theyhave been described previously in the present text, has not beenmodified for all that in its principle and the sealing characteristicscan benefit in each specific case by the radial offset of one of thethreadings, male or female one, between both sides of the zone of thecentral sealing means.

FIGS. 8, 9 and 10 show three embodiments of a coupled type connectionbetween two pipes each using two connectors of the invention.

FIG. 8 shows an axial cross section passing through axis X4—X4 ofconnection 48 of two pipes 49, 50 using a coupling 51.

Each pipe to be connected 49, 50 comprises a male element 53, 54 at itsend.

Coupling 51 is provided with a central stop-lug 52 and each end ofcoupling 51 comprises a female element 55, 56.

The respective association of elements 53-55 and 54-56 each constitute aconnector of the invention.

Male elements 53, 54 and female elements 55, 56 are such that theirstructure corresponds to the description which was made above and whichassociated together each constitute a connector of the invention. Inthis case, as in FIG. 4, each connector comprises a second sealing means59, 60 of the type described at 33 in FIG. 4 in addition to the centralsealing means 57, 58.

The stop means for stopping makeup of the male element into the femaleelement in a set position is constituted here by a stop-lug 52 ofcoupling 51 which acts as an abutment 61, 62 of the same type as theabutment shown at 30 in FIG. 4.

The connection of the invention is thus constituted by two connectors,also of the invention.

FIG. 9 is a variation of the embodiment of FIG. 8 and shows an axialcross section along X5—X5 of a connection of the invention connectingtwo pipes 63, 64 via a coupling 65.

In contrast to FIG. 8, coupling 65 does not include a lug like stop-lug52 in FIG. 8.

In this case the two connectors of the invention, constituted byrespective male and female elements 66-67 and 68-69 which form theconnection, include a common abutment 70 formed by bringing the ends 71,72 of male elements 66, 68 into bearing contact with each other.

This common abutment constitutes a common means for these two connectorsof the invention to stop make up at a set position to cause the male andfemale bearing surfaces of the central sealing means 73, 74 of eachconnector to coincide perfectly.

Further, a second sealing means is provided at 75, 76 in the centralzone of the coupling beyond the threaded zones of the connectorsconstituting the connection which here is produced in known manner bymetal-metal bearing of the two interfering surfaces which are tapered,for example.

To increase the precision of the central positioning of the commonabutment 70, steps 77, 78 are produced in the form of shoulders both onthe male element 66, 68 of each connector forming the connection and onthe female element 67, 69.

The axial distance between the female shoulders formed in coupling 65 isarranged so as to be slightly smaller than the axial distance betweenthe male shoulders when ends 71, 72 of male elements 66, 68 are bearingon their common abutment 70, such that these shoulders never oppose thebearing contact of ends 71, 72 of male elements 66, 68.

FIG. 9 also shows that only one side of step 77 of the male and femaleshoulders are in contact, a slight axial play existing on the side ofstep 78 between the corresponding male and female shoulders.

The position of the respective male and female shoulders of steps 77, 78are arranged so that the common abutment 70 is formed during makeup inthe central portion of the coupling, i.e., on the plane of its axis ofsymmetry Y1—Y1 or in the immediate vicinity thereof.

FIG. 10 is a variation of the embodiment of FIG. 9 and shows an axialcross section along X6—X6 of a connection of the invention joining twopipes 79, 80 via a coupling 81.

In contrast to FIG. 9, the two connectors of the invention constitutedby respective male and female elements 82-83 and 84-85 which form theconnection each comprise only their central sealing means 86, 87.

In contrast to FIG. 8 and 9, there is no second sealing means.

The connection also comprises a common abutment 89 and steps 90, 91formed both on the male elements 82, 84 and on female elements 83, 85which act to precisely position this abutment 89 in or close to theplane of symmetry Y2—Y2 of the coupling.

The desired axial play is provided so that these steps functionanalogously to that described for FIG. 9.

In contrast, central zone 88 of the connection does not have a sealingsurface and the non threaded end of male elements 82, 84 slide with freeradial play in the central zone 88 of coupling 81 until abutting at 89.

Clearly, a connection of two pipes of the integral type can be made inaccordance with the invention using a single connector of the invention.

For such a connection reference should be made to FIGS. 1 and 2, forexample as well as to FIGS. 3 and 4.

In this case, each pipe 3, 4 to be connected carries alternately at itsends a male element or a female element of the invention and theconnection is made by making up a male element 1 on one end of a firstpipe 3 into a female element 2 at one end of a second pipe 4.

As has been shown in the above description, the connector of theinvention and the connections produced with these connectors areparticularly compact while having the desired external and internalsealing qualities.

This results from the fact that the threading is constituted by a singlethreaded zone, without a break in alignment of the taper on which theyare formed, in contrast to existing connectors comprising two radiallyand axially offset threaded zones.

Further, because of the position of the central sealing means, theperfect threads of the threading can be extended to the two ends when nosecond sealing means is added.

This means that the tension efficiency (critical section) of theconnector is higher than that of the connector of the same dimensionswith sealing surfaces at the ends of the threadings.

Clearly, the taper of the threading is selected so that the male elementengages easily in the female element.

Advantageously and in a non limiting manner, threadings are selectedwherein the slope with respect to the axis is 2.86° or more.

The connector and connection of the invention, which are intended toresist high pressures, will usually but not exclusively be produced fromthick, large diameter pipes.

A large number of variations of the invention can be made, all of whichare within the scope of the claims of the present patent.

What is claimed is:
 1. A threaded pipe connector comprising a maleelement disposed at an end of a first pipe and a female element disposedat an end of a second pipe and a sealing means, the male elementcomprising an external tapered male threading and the female elementcomprising an internal tapered female threading which corresponds to themale threading, wherein the male threading comprises a single malethreaded zone disposed on a surface generated by a first straight lineof a first cone and the female threading comprises a single femalethreaded zone disposed on a surface generated by a second straight lineof a second cone, and the sealing means is a central sealing meansformed by a male bearing surface and a female bearing surface which canbear on each other in a connected position of the connector, the maleand female bearing surfaces being disposed in a globally central zone ofthe male threaded zone for the male bearing surface and of the femalethreaded zone for the female bearing surface within which the respectivemale and female threadings are interrupted, a stop means also beingprovided to stop makeup of the male element in the female element in aset position in the connected position of the connector.
 2. A connectoraccording to claim 1, wherein the male threaded zone and the femalethreaded zone include both perfect threads and threads with imperfect orvanishing or incomplete ends.
 3. A connector according to claim 1,wherein the central sealing means is disposed in a zone which extendsfrom a mid point of the male or female threaded zone by a length at mostequal to ¼ of a length of said threaded zone to each side of said midpoint.
 4. A connector according to claim 1, wherein the stop means whichcan stop makeup of the male element into the female element in the setposition in the connected position of the connector is constituted by ameans directly linked to the threadings.
 5. A connector according toclaim 1, wherein the stop means which stops makeup of the male elementinto the female element in the set position in the connected position ofthe connector is constituted by a means which is independent of thethreadings.
 6. A connector according to claim 5, wherein the means whichis independent of the threadings comprises an abutment.
 7. A connectoraccording to claim 1, wherein at least one of the bearing surfaces, themale surface, or the female surface of the central sealing means isconstituted by a tapered surface, a taper of which is in a samedirection as a taper of the threading, and wherein an angle with respectto an axis of the connector is larger than an angle of the taper of thethreading with respect to the axis.
 8. A connector according to claim 7,wherein the angle of the tapered bearing surface with the connector axisis larger by a value of at most 20° than the angle of the taper of thethreading with respect to the axis.
 9. A connector according to claim 1,wherein a maximum spatial requirement of the male and female bearingsurfaces is defined by a space existing between generatrices defininglimits of the maximum spatial requirement of the threadings.
 10. Aconnector according to claim 9, wherein a portion of the generatricesdefining the limits of the maximum spatial requirement of the threadingswhich is located on one side of the central sealing means is for one ofthe threadings, the male or the female one, slightly radially offsetwith respect to an axis of the pipe of a portion of a same generatrixlocated on another side of the central sealing means.
 11. A connectoraccording to claim 1, wherein the male bearing surface and the femalebearing surface of the central sealing means comprise two taperedsurfaces, and the taper of the sealing means is greater than the taperof the male and female threadings.
 12. A connector according to claim 1,further comprising a second sealing means.
 13. A connector according toclaim 12, wherein the second sealing means is provided by a male bearingsurface located close to a free end of the male element and a femalebearing surface located on a corresponding portion of the femaleelement, the male and female surfaces coming into bearing contact witheach other during makeup of the connector.
 14. A connector according toclaim 1, wherein interference at the male and female bearing surfaces ofthe central sealing means is higher than interference between the malethreading and the female threading.
 15. An integral type threadedconnection for first and second pipes, produced by a connector accordingto claim 1, the male element of the connector being formed at an end ofthe first pipe, the female element being formed at an end of the secondpipe.
 16. A connection according to claim 15, wherein the female elementis produced at one end of the pipe which has been expanded, the maleelement being produced at one end of the pipe which has been thickened.17. A threaded and coupled type connection for first and second pipes,produced by two connectors according to claim 1, one male element beingformed at each end of the pipes, a female element being produced at eachend of a coupling, one male element of each pipe being connected in eachfemale element of one end of the coupling.
 18. A connection according toclaim 17, wherein in the connected position, the free end of each maleelement comes into bearing contact with a portion of the couplingforming a central stop-lug to produce two abutments.
 19. A connectionaccording to claim 17, wherein in the connected position, two free endsof the male elements come into bearing contact with each other thusforming a common abutment.
 20. A connection according to claim 19,wherein steps forming shoulders are formed in each male element and eachfemale element close to the central portion of the coupling, whichshoulders enable said common abutment to be precisely positioned.